Brown announced Monday at a news conference in Largo that Jim Messina will help on all aspects of the campaign. That includes volunteer organizing and fundraising.

Brown also announced that he has raised $1 million since the end of the legislative session in mid-April.

Brown will likely be challenged for the Democratic nomination by Maryland Attorney General Doug Gansler, whose formal announcement is expected in September.

Montgomery County Del. Heather Mizeur also is planning to run. Rep. C.A. Dutch Ruppersberger is considering a bid.

Maryland's primary is nearly a year away in June.

Last month, Brown officially named Howard County Executive Ken Ulman as his running mate. Republican Harford County Executive David Craig and Del. Ron George, an Anne Arundel County Republican, have also officially announced their candidacy.